Many liquid-propellant rockets use cryogenic fluids, such as liquid fuels, e.g. liquid hydrogen, and liquid oxygen, as propellants, and it is necessary to keep the propellant feed temperature and the device temperature required for engine ignition low.
A fluid cooling system 3 that maintains the propellant feed temperature in a liquid-propellant rocket will now be described with reference to FIG. 4. The fluid cooling system 3 is used in a second-stage rocket that carries an artificial satellite, etc. and travels by inertia around a planet while correcting its orbit.
When the second-stage rocket is traveling by inertia through outer space, a feed line 6 that feeds a propellant from a storage tank 4 to a pump 8, main lines 9 and 11 that feed the propellant from the pump 8 to an engine (not shown) connected to the main line 11, and an internal fluid increase in temperature due to heat input from the outside or from the pump 8. The fluid cooling system 3 discards the propellant to the outside (i.e., outer space) at regular intervals after the propellant has reached a saturation temperature or higher due to the heat input from the outside and accumulated in the feed line 6 and the main lines 9 and 11. By discarding the propellant outside, the interior of the feed line 6 and the main lines 9 and 11 is replaced with the low-temperature propellant from the storage tank 4.
In the case of the fluid cooling system 3 shown in FIG. 4, when the second-stage rocket is traveling by inertia without combusting the propellant in the engine, a main valve 10, a precooling valve 14, and a bearing precooling valve 16 are normally set in a closed state. When the propellant is to be replaced while the rocket is traveling by inertia, the precooling valve 14 and the bearing precooling valve 16 are opened so that the propellant accumulated in the feed line 6 and the main line 9 is discarded outside via an exhaust pipe 13 and an exhaust port 18.
Non Patent Literature 1 discloses a technology for precooling a fluid by discarding the fluid little by little and continuously replacing the fluid in the pipes.